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Charter Member
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Discussion Starter #1
Just got some new folks that moved in next door. Seems like he's going to be the mister know it all type, but I'll give him a second chance. Anyhow, wanting to take a quick run to the store, upon returning to the house, the guy catches me in the garage and says It seems to be running rich. It was his first time seeing the cobra. Now Ive had my car for awhile and this is not the usual response I get. So I tell him that my car does what it feels like at the time, because it is EFI. He recommened a tuneup in a can that they sell at azone. Im only three years experience with EFI. Now the question. Is it possible to be running rich with an EFI. Three notes. I have a 347, and I have film while running at the drag strip that shows a very small noticible puff of smoke at shift points, and last when I let off of the gas while in gear the car does pop like a harley bike, but not an out of tune pop. Any help is apreciated. Running at 14 degrees. I use nos now and again.
 

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Senior Member
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6,546 Posts
Yes, they can run rich..and you should run it a little on the rich side with NO2. That's quite a bit of timing for NO2 as well.

That tune up in a can stuff is snake oil.

Assuming your car is tuned pretty closely to optimal my bet is that he is most likely confusing the difference in exhaust odor between his car with catalytic converters and yours that does not have them.
 

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FFCobra Fanatic
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742 Posts
"That tune up in a can stuff is snake oil."
Is that good?

Anyways, Ozono is right. That and the question I have for you is if you are running O2 sensors. Not running these with EFI will have the car run rich until I believe the engine gets to running temp., then the idle and overall performance of the car returns somewaht to normal...I think, could be wrong.

Either that, or the guy wanted to sound important...
 

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FFCobra Master Craftsman
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1,123 Posts
Yes, they can run rich on EFI, and you are much better off running rich than lean. The puff of smoke you are seeing doesn't necessarily mean that it is running excessively rich. The Cobra will smoke more (than a 'normal' car) due to lack of the emission controls (you don't have cats or smog pump, right?).
 

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Charter Member
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Discussion Starter #5
Thanks guys. No pump. Im running sensors. not sure if they work or not. Bought some new ones when the engine was rebuilt. By the way how do you know if they are working or not. What about the popping when decelarating (not sure if this is the correct spelling.) Thought I heard a thread about eliminating this. Any thoughts.
 

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FFCobra Fanatic
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1,808 Posts
If it's running rich that's good. You can usually tell by the smell and some black smoke right as you fire it up. If you don't have a fuel pressure guage I would recommend installing one. You can really run into some problems if you run it on the lean side so tell Mr. Know-it-all that by design your high compression engine is designed to run a little rich to take advantage of the HP and lack of emission equipment.
 

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FFCobra Fanatic
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2,266 Posts
John,

You mention youre running a 347 but don't mention what other upgrades over stock (heads, cam, intake, etc.). You also don't mention which EFI you are running so its hard to comment a whole lot. As mentioned you can certainly be running rich or lean or both depending on when you measure it. Share more about your setup and someone might be able to share more specific valuable insights...

-Matt
 

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19# injectors seem small for your engine setup. They shouldn't have an impact on your car running rich but I would think that you maybe starving your engine of fuel up top. I would suggest 24#s.(and all accesories to go with them)
A dyno tune to see what your air/fuel ratio is may help a lot.
I'M NOT A GURU so I'll let someone put in more info on what I've said. Just some of my ideas now hopefully someone agrees with me or calls me an A$$ for giving bad info. Either way we both learn a little more! :D
Adam
 

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Zipper-suited sun god and
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2,033 Posts
I second the dynotune. Nothing like a wideband O2 sensor to tell if you're actually running rich or not. You can also check to see if your O2 sensors are working by pulling the codes from the EEC. If they're acting up there should be a code in the computer.
 

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FFCobra Craftsman
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I'm not a guru either but,,,If you fired up your car stone cold and took off,,,it might be the injection compensating for the cold motor (like having a choke).
 

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FFCobra Fanatic
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2,266 Posts
John,

Some good advice. Here is what I would do first.

1. As mentioned check the codes. A bad sensor such as O2, or ECT (engine coolant) can result in a rich condition.

2. Take it to a dyno and have the A/F ratio checked. Since we don't run crossover pipes do 2 pulls with the wideband sensor on each side. 2 pulls on right 2 pulls on left. Probably only cost you $70 or so just for the pulls and a/f.

Given your stroked with ported heads and other mods I doubt being rich is a concern. In fact I'd almost be willing to bet that if you have never had a dyno/chip tune your running lean with those injectors. The 19 lb injectors arn't good for much more than 300-325hp. Also, if you havn't already be sure your stock fuel pump is replaced as its only good for 280 to 300hp tops.

With a stroked setup with those mods you are almost certainly going to need a chip tune. The EEC-IV system is pretty felixible and can adapt to a point. Once you get into heavy mods particularly stroking or forced induction you take it beyond what the computer can compensate for with the stock calibration. If you change the injectors consider keeping a MAF (even if you replace it) that is calibrated as stock (19lb) as opposed to buying one that is designed to fool the computer by altering the output voltage. Instead, get a chip burned that will compensate for the larger injectors. This is a much better way to introduce larger injectors. If you do it by installing a MAF that has been tweaked to fool the computer the a/f will not be correct in all operating conditions.

Good Luck.

-Matt
 

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Senior Charter Member
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1,600 Posts
10sec?ride,
One other thing...the popping that your hearing when you let off the gas is called "backing down" and it means that you have a free flowing exhaust system. Its' a good thing.

Take care,
Ron
 

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FFCobra Fanatic
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592 Posts
John,
I too am running a 347 with ported rpm heads and rpm intake, however I am running 30lbs injectors and the car runs good on them, maybe a little rich but as mentioned before, thats better than too lean. By the way what kind of times are you turning with and without the nitrous.
 
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